Fluid-operated piston for metering gravity fed material

ABSTRACT

A pump piston in one cylinder is connected with a power piston operated by compressed air in a second cylinder rigid with the first, and a common rod connecting the pistons extends from the second cylinder so an adjusting screw abutting its end serves to give fine adjustments to the stroke to give accurate measurement of the amount of slurry dispensed in each operation. The slurry is delivered by gravity to the pump cylinder, and air operated valves control the communication between the pump cylinder and the gravity supply conduit and also between said cylinder and a discharge nozzle, where an air operated plunger clears the nozzle of slurry at the end of each discharge. A servo valve cooperates with two trip valves to control the air flow for operating the power piston, as well as the air-operated valves and nozzle plunger, one trip valve being operated automatically at the end of the forward stroke of the pistons to start the return stroke and the other being either operated automatically by a can moving into filling position or at the end of the return stroke of the pistons. The servo valve is of novel plastic construction, as are also the two trip valves. In the servo valve, the reciprocable slide valve is of a plastic material having appreciable lubricity in relation to the plastic material of the seat for easy operation and long wear, while in the trip valves both the body part with the valve projection on it and the fulcrummed arm that carries a valve seat gasket are of extremely hard rigid plastic material to avoid any flexing of the arm in the opening of the trip valve against the resistance of its return band, close accuracy of movement of this arm both ways being important for close accuracy of measurement of the material dispensed.

Ilnited Mates Rutheriord Ian. 25, I972 [541 FLUID-OPERATED PISTON FURMETERING GRAVITY FED MATERIAL Russell G. Rutherford, 8045 Beach Drive,Rockford, ill. 61 103 [22] Filed: Feb. 9, 1970 [21] ApplNo; 9,553

[72] Inventor:

Primary Examiner-Stanley H. Tollberg AttorneyAndrew F. Wintercorn 57ABSTRACT A pump piston in one cylinder is connected with a power pistonoperated by compressed air in a second cylinder rigid with the first,and a common rod connecting the pistons extends from the second cylinderso an adjusting screw abutting its end serves to give fine adjustmentsto the stroke to give accurate measurement of the amount of sllurrydispensed in each operation. The slurry is delivered by gravity to thepump cylinder, and air operated valves control the communication betweenthe pump cylinder and the gravity supply conduit and also between saidcylinder and a discharge nozzle, where an air operated plunger clearsthe nozzle of slurry at the end of each discharge. A servo valvecooperates with two trip valves to control the air flow for operatingthe power piston, as well as the air-operated valves and nozzle plunger.one trip valve being operated automatically at the end of the forwardstroke of the pistons to start the return stroke and the other beingeither operated automatically by a can moving into filling position orat the end of the return stroke of the pistons. The servo valve is ofnovel plastic construction, as are also the two trip valves. In theservo valve, the reciprocable slide valve is of a plastic materialhaving appreciable lubricity in relation to the plastic material of theseat for easy operation and long wear, while in the trip valves both thebody part with the valve projection on it and the fulcrummed arm thatcarries a valve seat gasket are of extremely hard rigid plastic materialto avoid any flexing of the arm in the opening of the trip valve againstthe resistance of its return band, close accuracy of movement of thisarm both ways being important for close accuracy of measurement ofthematerial dispensed.

7 Claims, 8 Drawing Figures PMENTEDJANZSIBYZ 3,637,116

. sum 1 UP a //V VE/V7'0R RUSSELL G. RUTHERFORD A T TOR/VE Y PATEMEUJANZSIHYZ SHEEE 30? 4 //v VE/V 70R. RUSSELL a EU THERFORDI assmlsPATENIEU M25 1372 SHEET u OF ..//Vl/E/V70R.'

RUSSELL 6. RUTHERFORD ATTORNE FLUID-OPERATED PISTON FOR METERING GRAVITYll lEll) MATERIAL This invention relates to a measured slurry dispenser,which, while specially designed for use in canning plants to dispensevarious kinds of slurries in accurately measured amount into each can asit is fed to the filler in a canning line and constructed to assurecontinuous operation properly in such humid environments, whereelectrical components would not be at all satisfactory, making pneumaticoperation the ultimate in reliability, and requiring operation as fastas the can fillers, even on lines handling up to about 120 cans perminute, is not limited to that specific application, inasmuch asmaterials varying either way from a medium slurry may be dispensed andthe amount dispensed at each operation is variable to suit practicallyany requirement that might arise.

The versatility of the present dispenser in the dispensing of light,medium, and heavy slurries, is best emphasized by listing below typicalmaterials that can be, and have been dispensed:

mashed potatoes jellies meat slurries potato salad honey coleslawcalking cement molasses fruit salad peanut butter paints cream herringcom relish glues chop suey cottage cheese syrups chow mein cheesespreads sausage barbecue crock cheese hamburger cream cheese picklerelish butter shrimp cocktail pic fillings harvard beets cream spinachjams salad dressings pumpkin fruit slurries candied fruit cream cornmacaroni dc cheese macaroni salad hand cleaner Salient features of thepresent dispenser are:

1. It is fully automatic in that the unit offers the all important-nocan, no fill-feature;

2. It is easy to take apart for cleaning and servicing;

3. A manually operated volume control adjustment at one end of the aircylinder accurately predetennines the intake stroke of the air pistonand accordingly of the slurry piston so that infinite adjustment as tovolume of slurry dispensed is made possible, and, once the desiredadjustment is obtained a locknut on the adjusting screw can be tightenedto eliminate any likelihood of alteration accidentally or otherwise, and

4. Two trip valves of performance. tappet-type construction cooperatewith a two-position reciprocable slide valve to control the pneumaticoperation of the slurry dispenser, one of the trip valves beingpreferably operated by engagement by each can as it arrives in fillingposition, and the other being preferably operated at the end of thedischarge stroke of the slurry and air pistons so that there is perfecttiming and no lost motion as the reciprocating valve moves one way inresponse to deflection of the first valve and the other way in responseto deflection of the second valve, to cause the air piston to move onthe discharge stroke in the first instance and on the intake stroke inthe second instance, neither of the valves being subject to stickinglike so many plunger valves and all of them being easier to clean andkeep clean and being in no way subject to the common objection that wearthrough ordinary usage impairs their usefulness and gives rise toleakage and unreliable performance,

The invention is illustrated in the accompanying drawings,

in which:

FIG. 1] is a perspective view showing a typical slurry dispensinginstallation using the measured slurry dispenser of my invention;

FIG. 2 is a perspective view of the back plate behind the air cylindershowing the second trip valve arranged to be operated by the projectingend of the air piston rod at the end of the forward stroke of the slurryand air pistons to start the rearward movement thereof for the intakestroke of the slurry piston;

FIG. 3 is a cross section through one of the trip valves;

Referring to the drawing and at first mainly to FIG. ll,

FIG. d is a vertical section through the slide valve that is operativelyassociated with the two trip valves;

FIGS. 5 and 6 are cross sections on the lines 5-5 and 6-6, respectively,of FIG. 4, and

FIGS. 7 and 8 are diagrammatic views of the dispenser showing the partson the intake stroke in FIG. 7 and on the discharge stroke in FIG. 8,the latter figure having indicated in dotted lines an alternativearrangement of one of the trip valves, whereby both of the trip valvesare operable by the piston rod at opposite ends of the stroke thereofinstead of having the second trip valve operated by a can as it arrivesin filling position.

Referring to the drawings and at first mainly to FIG. I, the referencenumeral 9 designates the measured slurry dispenser of my inventiongenerally, which is shown adjacent a filler 10 in a canning plant, cansllll being delivered to the tiller one by one on a belt 12, the forwardindexing of which is timed with the operation of trip valves 13 and Mand the related servo valve 15 so that in the pauses between these indexmovements the foremost can 11 disposed in the station below the nozzle16 will receive its measured amount of slurry, as indicated at 17 inFIGS. 1 and 8, from the nozzle 16, the can being then moved forwardly bythe next can outof the way to allow positioning of this next can in thatsame station. The cans 11 are conveyed to the filler in any suitable wayfrom a supply source for final discharge down a chute (not shown)leading to the belt 12, so that there will always be another can readyto receive the slurry discharged from the nozzle 16. Should there be afailure of supply of cans for any reason, the trip valve 13 which isoperated automatically by the oscillation of the arm 13 against theresistance of a tension spring or rubber band 19 by abutment of theforemost can ill with the arm 18, as shown in FIG. ll, willautomatically shut off the dispensing of the slurry and stop the filler10 until a fresh supply of cans is provided. The compressed air foroperating the dispenser 9 is delivered to the servo valve 15 through aflexible hose 20 connected with a pipe in the canning plant air supplysystem, a gauge 211 at the point of connection of hose 20 with valve 15indicating the air pressure to the operator, so that, in starting up, ifthere is insufficient air pressure indicated by the gauge 21 to operatethe dispenser 9, the operator can hold up the feeding of cans Ill to thetiller 10 until the right pressure is indicated. A handle 22 operates anair shutofi" valve 23 provided on the back of the gauge 21. With eachretracting movement of the arm 18 under action of the encircling springor rubber band 19, air is delivered, as shown best in FIG. 7, from theservo valve 15 through a flexible hose 24 to the forward end of the aircylinder 25 to force the piston 26 therein to the rear, and, by virtueof the latters rod connection 27 with the piston 28 working in theslurry cylinder 29, pump a measured amount of slurry from a gravitysupply tank (not shown) through a supply tube 30 (FIG. ll) into thecylinder 29. Then, when the foremost can llll engages and moves the arm18 of trip valve 13 forwardly against the action of the spring or band19, this measured amount of slurry will be discharged from the cylinder29 through the nozzle 16 by reason of air being discharged through theflexible tube 31 to the rear end of the air cylinder 25 to force thepiston 26 forwardly and with it piston 28 in cylinder 29 on thedischarge stroke. Hose 24 serves as an exhaust line during the forwardmovement of piston 26, and hose 31 serves as an exhaust line during therearward movement of piston 26.

The servo valve l5 also controls the pneumatic operation ofinterconnected pistons 32 and 33 working in cylinders 34 and 35,respectively, to reciprocate the plunger valves 36 and 37 slidable inbores 36' and 37' in the valve body 38 to control communication betweenthe ports 39 and d0 provided in the body 38 and also controlcommunication of the supply tube 30 with port 39. Thus, on the intakestroke of the slurry piston 28, as shown in FIG. 7, slurry is suppliedto the cylinder 29 past the plunger valve 37, which, as clearly appears,is connected by the reduced rod connection 41 with the plunger valve 36,the latter in this position of valve 37 shutting off port 40 fromcommunication with port 39 and discharge tube 42 so that there isnothing to interfere with the combination of gravity and suction in thefilling of the slurry cylinder 29 in front of piston 28. However, on thedischarge stroke, as seen in FIG. 8, the valve 37 shuts off the tube 30while valve 36 opens communication between the ports 39 and 40 to permitdischarge of slurry through tube 42. Operation of pistons 32 and 33requires only the two flexible tubes 43 and 44 extending from the servovalve 15 to the outer ends of cylinders 34 and 35.

A piston 45 is reciprocable in a cylinder 46 with which flexible tubes47 and 49 are connected at opposite ends, the tubes extending from theservo valve 15. Piston 45 operates a plunger valve 49 in the bore 50 ofthe valve body 51 in either direction to close off communication withthe discharge tube 42, as shown in FIG. 7, and at the same time expelwhatever slurry would otherwise remain in the bore 50 at the end of thedischarge stroke illustrated in FIG. 8, where the plunger valve 49 isshown in its fully retracted position during the discharge stroke ofpiston 28. A port 52 in the valve body 51 provides communication betweenthe discharge tube 42 and the bore 50 in which the plunger 49 operates.

In describing the operation, it should first be noted that the servovalve 15 comprises a reciprocable slide 53 valve member of circular formhaving a circular recess 54 large enough in diameter to overlap thecenter port 55 in the base 56 along with either of the side ports 57 and58, so that in one position, as for example the intake stroke of piston28, shown in FIG. 7, compressed air is delivered from pressure chamber59 through port 57 and tube 24 to the air cylinder 25 to move the piston26 to the rear and operate the piston 28 on its intake stroke, while atthe same time operating the valve 49 by means of piston 45 to expel intothe can 11 whatever slurry might otherwise remain in the bore 50, thevalves 36 and 37 also being shifted to shut off the outlet port 40 andopen the inlet port 39 to the tube 30 by virtue of the delivery ofcompressed air through tubes 47 and 43, while tubes 31, 44, and 48 areall placed in communication with the exhaust port 55 so as not tointerfere with movement of the pistons 26, 33, and 45. Then, as shown inFIG. 8, with the valve in its other extreme position for the dischargestroke, compressed air is delivered from chamber 59 to tubes 31, 44 and48 to cause the reverse operation of pistons 26, 33, and 45, while thetubes 24, 43, and 47 are all placed in communication with the exhaustport 55 so as not to interfere with operation of the pistons mentioned,the piston 28 in the forward movement of piston 26 serving to dischargean accurately measured amount of slurry into the can 11 while valve 37cuts ofi communication with tube 30 for port 39, and valve 36 openscommunication between ports 38 and 40 for free flow of the slurrythrough the discharge tube 42 and nozzle 16 into can 11, valve 49 havingbeen retracted to uncover port 52.

Trip valves 13 and I4 serve to operate the slide valve 53 by unbalancingthe air pressure on the remote ends of the interconnected pistons 60 and61 operating in cylinders 62 and 63 that open into the pressure chamber59, trip valve 13 having a flexible hose connection 64 with cylinder 63,while trip valve 14 has a flexible hose connection 65 with cylinder 63.Thus, when either of these trip valves is operated a port 80 in valveprojection 81 normally sealed by a resilient compressible gasket 82 ofViton or the like is opened and the cylinder connected with that port isopened, of course, to atmosphere so the pistons 60-61 move in thatdirection under air pressure, accordingly moving the slide valve 53 bymeans of its pin and hole connection 66-67 in the same direction. Thus,in FIG. 7 with trip valve 13 closed and trip valve 14 open, slide valve53 is in the one extreme position for the intake stroke of piston 28,whereas in FIG. 8, with trip valve 13 open and trip valve 14 closed,slide valve 53 is in the other extreme position for the discharge strokeof piston 28.

The cylinders 62 and 63 are provided in the body 68 of the servo valve15 which is suitably secured in airtight relationship to the base 56, asby means of bolts 69, as indicated in FIGS. and 6, the projectingcylindrical neck 70 on the base 56 that fits snugly in the bottom of thecylindrical pressure chamber 59 and the rubber O-ring 71 that surroundsthe neck and is set in an annular groove provided in the base 56 aroundthe neck so as to be compressed when the two parts 56 and 68 of thevalve are fastened together, serving to insure a good airtight sealingaction. In a similar way, caps 72 are fastened to opposite sides of thebody 68 on flats 73 provided therefor and compress rubber O-rings 74that are interposed to provide a good airtight seal at these joints.Now, it is important to mention that the bushings 75 that I haveprovided in the cylinders 62 and 63 are of polyethylene, as is also thedouble-end piston 60-61 and the slide valve 53, whereas all of the otherparts of the servo valve 15 are of polypropylene, the purpose of thisbeing that polyethylene has the characteristic of high lubricity whichis so desirable in the double-ended piston 60-61 and slide valve 53,whereas polypropylene, which defines the flat seat 76 integral with thebase 56 on which the slide valve 53 operates, is approximately 60percent harder than the polyethylene and has little or no lubricity,with the result that the slide valve 53, which relies upon the airpressure to hold it seated at 76 and is held positioned on said seat byreason of the engagement of its flat top surface 77 on the bottom of thereduced connecting portion 78 between the pistons 60 and 61, thus beingfree to turn with its stem 66 as a center, is selflubricating and willgive extremely long satisfactory service before it needs replacement.Replacement of such a small part as the slide valve 53 means apractically negligible outlay compared, for example, to the cost ofreplacing the base member 56, or for that matter any other part of theservo valve 15. In passing, attention is also called to the rubberO-rings 79 provided in annular grooves in the pistons 60 and 61 whichserve to prevent leakage of air along the pistons 60 and 61 from thepressure chamber 59 in either position of the valve 53.

A feature of importance, only from the standpoint of enabling completecleaning, bearing in mid the fact that the present invention is used inthe canning industry, is the provision of the restricted vent holes 82radially of the reduced portion 78 and communicating with the axialbores 83 provided in the opposite ends of the double-ended piston 60-61to save material and make for lightness. These vent holes 82 provide fordrainage of cleaning solution and rinse water when the servo valve 15 istaken apart and cleaned.

The trip valves 13 and 14 are both alike so that description of valve13, shown in FIG. 3 will suffice for both. Each of these valvescomprises a generally rectangular elongated plastic body 84 having atransverse V-groove 85 provided therein intermediate the ends thereof,in longitudinally spaced relation to the generally frustoconical valveprojection 81, previously mentioned, the V-groove receiving in thebottom thereof the sharp straight edge portion of a generally V-shapedfulcrum projection 86 provided on the arm 18 transversely thereofintermediate the ends and in longitudinally spaced relation to acircular recess 87 in which the circular gasket 82, previouslymentioned, is fixed, this gasket, as previously described, forming anairtight valve seat for the valve projection 81. An encircling rubberband (or spring) 19 serves nonnally to keep the valve closed and isdisposed between the fulcrum projection 86 and the gasket 82 and heldagainst displacement in either direction longitudinally of the tripvalve by engagement in the grooves provided transversely of the twoparts 18 and 84, as indicated at 88 and 89, respectively. Now, it isimportant to mention that the two valve parts 18 and 84 are both moldedof polyvinyl chloride, which is a great deal harder than polypropyleneand extremely rigid so that there is virtually no flexing of the arm 18when it is operated by engagement with a can 11, despite the loadimposed on the arm 18 by the band 19, immediate and complete response todeflection of the free end of arm 18 being important here because of (a)the need for close accuracy of measurement in the amount of slurrydispensed in each operation, and (b) the speed of operation of thedispenser, which allows for substantially no lag in the responsivenessof both trip valves 13 and 14. This trip valve construction is alsovirtually indestructible with normal usage and is very easily takenapart for thorough cleaning and as easily put together, the band 19being easily stretchable to the extent necessary to disassemble the arm18 from the body 841. The holes indicated at 90 extending transverselythrough the body 84 at one end thereof facilitate mounting the valve 13(or M) by means of bolts 91 on any support, as for example, a supportingbracket 92 in a substantially horizontal plane, as illustrated inFIG. 1. Of course, either of the trip valves may be secured by volts 93extending at 90 to the first mentioned bolts 91 through holes in theother end of the body portion, as shown in FIG. 2, where the trip valve14 is shown mounted that way on the backplate 94- of the dispenser 9,the arm 18 of that valve being arranged to be operated by a projection 91 on the projecting end portion 95 of the piston rod 27, as is alsoshown in FIGS. 7 and 8. The screw 96 is adjustable with respect to thefixed end plate 97 and arranged to be locked in its adjusted conditionby means of a locknut 98 to predetermine the exact amount of slurry thatwill be dispensed upon each operation of the dispenser by predeterminingthe length of stroke of pistons 26 and 28.

In conclusion, attention is called to the dotted line connection 64,shown in FIG. 8 between the servo valve and the dotted line showing of atrip valve 13, in lieu of the full line showing the trip valve 13. Withthat arrangement the projection 94 on the outer end portion 95 of thepiston rod 27 is arranged to operate the trip valve 13 at the end of theintake stroke of the pistons 26 and 28 to start the discharge stroke, inlieu of having the discharge stroke started by deflection of arm 18 by acan 11. Then at the end of the discharge stroke, the projection 94operates the arm 18 of the valve 14 to start the intake stroke,similarly as in the previous description. This arrangement is suitablefor a hand feed canning machine where the cans are fed one after anotherby hand as they are filled, or in an automatic machine where the merefilling of the cans to its predetermined weight causes automatic kickingof each filled can out of the way and automatic kicking of an empty caninto filling position. The intake stroke of the piston represents a timeinterval that is very short, but long enough to enable that kind ofoperation.

It is believed the foregoing description conveys a good un derstandingof the objects and advantages of my invention. While a preferredembodiment of the invention has been illustrated and described, this isonly for the purpose of illustration, and it is to be understood thatvarious modifications in structure will occur to a person skilled inthis art.

lclaim:

1. A dispensing apparatus of the character described comprising, incombination, coaxially arranged air and pump cylinders in fixedrelationship to one another with interconnecting pistons reciprocabletherein, one piston being a power piston operable back and forth in theair cylinder by compressed air, the other piston being a pump pistonadapted for drawing in flowable material on an intake stroke into thepump cylinder and discharging it on a return stroke, manually adjustablescrew means for limiting the return stroke of the power piston wherebyto predetermine the amount of material taken in and discharged by thepump piston in each reciprocation, a gravity source of flowable materialsupply above and connected with said material cylinder, a dischargenozzle, two-position valve means which in one position establishescommunication between said pump cylinder and said material supply sourceand in its other position establishes communication between the pumpcylinder and said discharge nozzle, a first piston and cylinder meansfor operating said two-position valve means by compressed air, a sourceof compressed air, a servo valve connected with the source of compressedair and including a reciprocable valve operable by a second piston andcylinder means by compressed air which reciprocable valve in oneposition supplies compressed air from said source to operate saidtwo-position valve means simultaneously with said power piston in onedirection for an intake stroke of the pump piston and in the otherposition supplies compressed air from said source to operate saidtwo-position valve means simultaneousl with said power iston in theppposite direction fort edischarge stroke oft epump piston, irst andsecond trip valves connected with opposite ends of said second pistonand cylinder means for alternately relieving air pressure on one or theother end for causing back and forth movements of said reciprocablevalve, said trip valves tending normally to close, means whereby one ofsaid trip valves is operated to open position automatically upon arrivalof said power piston at a predetermined position, and means foroperating the other trip valve to start an operating cycle.

2. A dispensing apparatus as set forth in claim 1 including incombination with the discharge nozzle of a two-position plunger valvewhich in one stroke clears the discharge bore of said nozzle of anyflowable material while cutting off its communication with said pumpcylinder on the intake stroke of its piston and in the return strokeopens communication between the discharge bore of said nozzle and saidpump cylinder on the discharge stroke of its piston, and means forreciprocating said plunger valve in timed relation to said pump piston.

3. A dispensing apparatus as set forth in claim 2 wherein the last-namedmeans comprises a third cylinder and piston means connected with saidtwo-position plunger valve and operable by compressed air from thereciprocable valve of the servo valve simultaneously with the othertwo-position valve means.

4. A dispensing apparatus as set forth in claim 1 wherein said tripvalves are operable to open position in response to arrival of saidpower piston at the opposite ends of its stroke.

5. A dispensing apparatus as set forth in claim 1 wherein said tripvalves are operable to open position in response to ar rival of saidpower piston at the opposite ends of its stroke, one of the trip valvesbeing adjustable relative to the other in accordance with the adjustmentof said manually adjustable screw means limiting the return stroke ofthe power piston.

6. A dispensing apparatus as set forth in claim 1 including a dischargeconduit between said pump cylinder and said discharge nozzle, saidtwo-position valve means comprising interconnected coaxial valveplungers reciprocable transversely relative to and between the adjacentends of said pump cylinder and said discharge conduit, these plungers inone position closing the end of said conduit but opening communicationbetween said pump cylinder and said source of flowable material, and inthe other position closing communication between said pump cylinder andsaid source of flowable material while opening communication betweensaid pump cylinder and said discharge conduit.

7. A dispensing apparatus as set forth in claim 1 wherein one of saidtrip valves is operated to open position automatically upon arrival ofthe power piston atone end of its stroke, the other of said trip valvesbeing operable in predetermined relationship to the first trip valve.

1. A dispensing apparatus of the character described comprising, incombination, coaxially arranged air and pump cylinders in fixedrelationship to one another with interconnected pistons reciprocabletherein, one piston being a power piston operable back and forth in theair cylinder by compressed air, the other piston being a pump pistonadapted for drawing in flowable material on an intake stroke into thepump cylinder and discharging it on a return stroke, manually adjustablescrew means for limiting the return stroke of the power piston wherebyto predetermine the amount of material taken in and discharged by thepump piston in each reciprocation, a gravity source of flowable materialsupply above and connected with said material cylinder, a dischargenozzle, two-position valve means which in one position establishescommunication between said pump cylinder and said material supply sourceand in its other position establishes communication between the pumpcylinder and said discharge nozzle, a first piston and cylinder meansfor operating said two-position valve means by compressed air, a sourceof compressed air, a servo valve connected with the source of compressedair and including a reciprocable valve operable by a second piston andcylinder means by compressed air which reciprocable valve in oneposition supplies compressed air from Said source to operate saidtwo-position valve means simultaneously with said power piston in onedirection for an intake stroke of the pump piston and in the otherposition supplies compressed air from said source to operate saidtwoposition valve means simultaneously with said power piston in theopposite direction for the discharge stroke of the pump piston, firstand second trip valves connected with opposite ends of said secondpiston and cylinder means for alternately relieving air pressure on oneor the other end for causing back and forth movements of saidreciprocable valve, said trip valves tending normally to close, meanswhereby one of said trip valves is operated to open positionautomatically upon arrival of said power piston at a predeterminedposition, and means for operating the other trip valve to start anoperating cycle.
 2. A dispensing apparatus as set forth in claim 1including in combination with the discharge nozzle of a two-positionplunger valve which in one stroke clears the discharge bore of saidnozzle of any flowable material while cutting off its communication withsaid pump cylinder on the intake stroke of its piston and in the returnstroke opens communication between the discharge bore of said nozzle andsaid pump cylinder on the discharge stroke of its piston, and means forreciprocating said plunger valve in timed relation to said pump piston.3. A dispensing apparatus as set forth in claim 2 wherein the last-namedmeans comprises a third cylinder and piston means connected with saidtwo-position plunger valve and operable by compressed air from thereciprocable valve of the servo valve simultaneously with the othertwo-position valve means.
 4. A dispensing apparatus as set forth inclaim 1 wherein said trip valves are operable to open position inresponse to arrival of said power piston at the opposite ends of itsstroke.
 5. A dispensing apparatus as set forth in claim 1 wherein saidtrip valves are operable to open position in response to arrival of saidpower piston at the opposite ends of its stroke, one of the trip valvesbeing adjustable relative to the other in accordance with the adjustmentof said manually adjustable screw means limiting the return stroke ofthe power piston.
 6. A dispensing apparatus as set forth in claim 1including a discharge conduit between said pump cylinder and saiddischarge nozzle, said two-position valve means comprisinginterconnected coaxial valve plungers reciprocable transversely relativeto and between the adjacent ends of said pump cylinder and saiddischarge conduit, these plungers in one position closing the end ofsaid conduit but opening communication between said pump cylinder andsaid source of flowable material, and in the other position closingcommunication between said pump cylinder and said source of flowablematerial while opening communication between said pump cylinder and saiddischarge conduit.
 7. A dispensing apparatus as set forth in claim 1wherein one of said trip valves is operated to open positionautomatically upon arrival of the power piston at one end of its stroke,the other of said trip valves being operable in predeterminedrelationship to the first trip valve.